1. Field of the Invention
This application relates to signal wires. More particularly, this application relates to insulation for signal wires.
2. Description of Related Art
PTFE (poly(tetrafluoroethene) or (poly(tetrafluoroethylene)) is one of the leading base dielectric materials used for insulation for high speed data cables because of PTFE's excellent dielectric constant, low dissipation factors, temperature performance range, and frequency stabilities. In addition, PTFE is unique as its dielectric constant depends on the degree of sintering (formation/curing).
Many cable designers have leveraged the low dielectric constant (about 1.6) of raw PTFE tape and extruded PTFE (w/o sintering) to produce high performance data cables. The industry has also generated an ‘expanded’ or ‘ePTFE’ technology to further reduce the dielectric constant. ePTFE is constructed by stretching unsintered PTFE to provide increased volume of PTFE. For example, cable designers and processors apply and use expanded PTFE both in taped PTFE and extruded PTFE applications as a dielectric to create superior high speed data cables. Many products use the combination of both raw PTFE (and expanded PTFE) to achieve very low dielectric constant, thus achieving high velocity propagation.
However, the dimension stability and performance stability of uncured and expanded PTFE tape construction is poor. For example, expanded PTFE suffers from very short use-life in coaxial cables and data bus cables due to the tendancy for short circuits between the center conductor and the braiding material. Such failures are often related to dynamic applications such as constant bending, vibration, and tight pinching. Like ePTFE, extruded raw PTFE dielectric in such applications also tends to crack after a few bending cycles, which also leads to the same failure mode.